Not only can you not turn off the sound; if you have muted macOS audio before starting Skype for Business, Skype will unmute your audio settings to about 20% just to make sure you hear this infernal sound. Stop adjusting my audio settings for me! I didn't ask you to do that!

We need to have mobile and desktop Skype for Business sync seamlessly. We need it to work perfectly just like normal Skype works. Presently, it seems that a college freshman programmed the Skype for Business sync feature.

Bottom line: Hey, Microsoft! Want revenue? Fix this. In todays standards, this is a basic feature. So do a good basic fix!